cluster-id/counter.js

Database cluster friendly object id with great query isolation.

var ref = require('./base64');
var encode = ref.encode;
var maxNum = ref.maxNum;

// return string in reverse order to increase variability of first symbols
function reverse (str) {
  return str.split('').reverse().join('')
}

function createCounter (counterLen) {
  var maxCounter = maxNum(counterLen)
  var counter
  var counterStartSecond

  function updateCounter (seconds, time) {
    if (counterStartSecond === seconds) {
      counter += 1
      if (counter > maxCounter) {
        counter = 0
      }
    } else {
      counter = time % maxCounter
      counterStartSecond = seconds
    }
    return counter
  }

  function encodeCounter (counter) {
    return reverse(encode(counter, counterLen))
  }

  return {
    updateCounter: updateCounter,
    encodeCounter: encodeCounter
  }
}

module.exports = createCounter